Method of and apparatus for heat treating steel articles



April 8, 1924;

H. F. wool:

METHOD OF AND APPARATUS FOR HEAT TREATING STEEL ARTICLES Filed Jan. 22. 1923 2 Sheets-Sheet 1 [i1 U071 for: Jyarmjd T. Zl/xmd 2 Sheets-Sheet 2 April 8, 1924;

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Patented Apr. 8, 1924.

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HAROLD E. WOOD, CHICAGO, ILLINOIS, v.ASSIGN'COIR- TO WYMA N-GORDO'N 00., OF WORCESTER, MASSACHUSETTS, A CORPORATION OF' MASSACHUSETTS.

ME HOD or mean 1-.

TUS FOR HEA TREATING STEEL ARTICLES.

Application filed January 22, '1923. Serial No. 614,072.

To all whom it may concern:

Be it known that I, HAROLD VVooo, a citizen of the United States, residing in- Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Methods of and Apparatus for Heat Treating Steel Articles, of

I vided with inte which the following is a specification.

This invention relates to the art of heattreating metals but more particularly to a new and improved method, of treating steel articles such as crankshafts for reciprocating engines, and has for its. primary object to provide'a simple and economical method of differentially hardening these. articles.v

In crankshafts such as are used in highspeed engines for automobiles, paeroplanes,

and the like, and particularly in those proadvantageous to ave the metal in different portions thereof possess different physical characteristics. The counterweights only require sufficient strength to resist the centrifugal force which tends to throw them. from the shaft during rotation. Adequate strength is obtained in the counterweights without any heat treatment. The crankshaft proper must be very carefully heat treated. The pins and bearings must be sufliciently hard to resist wear and the cheeks'must possess the necessary strength and toughness to withstand the great variety of stresses to which they are subjected in service.

Inasmuch as the crankshaft is forged from a single piece of steel of practically uniform chemical composition, it is evident that when the same is heat. treated, the entire forging will respond to such treatment in exact proportion to the relative sections of the same. This results in the'same degree of hardness throughout the forging, or as near uniformity as it is metallurgically possible to obtain. \Vhen a crankshaftin this condition is machined, difficulty is encountered in machining the -counterweights, due to the cuts being taken at a distance from the center of rotation and that the-same are intermittent cuts. This results in a substantial decrease in production and an in crease in cutting tool cost.

In my improved method of heat treatment, the entire article is heated to a temperature above the A0 thermal critical temperature. Certain parts of the article which do not require hardening are then cooled to a temral counterweights, it is Fig.1, and

perature below the hardening range while the remaining parts are retained within this range. The article is then quenched. The quenching causesthe parts which were retained within the hardenin range to be hardened but does not bar en the cooled parts. The article may then be reheated sufficiently to allow the transformation to complete itself to the desired stage. 7

V The many other objects and advantages of my invention will be better understood by reference to the following specification when considered in connectionwith the accompanying drawings illustrating one form of .apparatus which may be conveniently employed in carrying my invention into prac-' tice.

Referring to the drawings Fig. 1 is a plan View.

Fig. 2 is a side elevation, partially in section. 1

Fig. 3 is a section on the line 3-3 of Fi 1. p v

ig. 4 is a section on the line H of Fig. 5 is a plan view of the air supply apparatus.

' In the drawings is shown a multi-throw crankshaft forging 20 which has just been removed from the usual heating furnace and placed upon a suitable support 21 having positioning arms 19. This forging has been heated above the A0 thermal critical temperature sufliciently so that the crankshaft proper will remain above the Ar thermal critical temperature untilquenched, for the purpose to be explained. I prefer a temperature of about 1525 F. The crankshaft comprises bearings 22 cheeks 23, pins 24; and counterweights 25, the counterweights being forged integral with the crankshaft proper. The pins, cheeks and bearings are to be hardened in order that they may possess the necessary strength and wear-resisting qualities. The counterweights are not to be hardened as these are not subject to the more easily machined, as has been explained.

With this purpose in view, I next cool the counterweights to a temperature below the Ar thermal critical, while retaining the remainder of the crankshaft forging above the Ar thermal critical temperature or, in other words, within the hardening range of any considerable stress or wear andmay be temperature. It is immaterial to what extent this cooling is carried so long as the temperature of the cooling mass is reduced below the hardening range but I usually wait until the counterweights have reached a-black color. The cooling should preferably take place at a rate sufliciently slow to insure a complete transformation of the projectors comprise a casing having the wall or walls facing the counterweight or counterweights provided with a plurality of perforations so that the air blast will be properly distributed over the opposing surface of the counterweights. These projectors are connected by means of pipes 27 with a source of compressed air supply and the air volume is regulated by means of a standard valve 28 located at some convenientpoint in the piping. It has been found in practice that this method of cooling the counterweights does not materially reduce the temperature of the crankshaft proper and that no difliculty is encountered in. maintaining it within the' hardening range if the entire forging is adequately heated'in the initial operation.

. I.The entire crankshaft forging is now -tion of the counterweights make cooling fql lienched. This quenching causes the cranks aft proper to harden but no hardening takes place in the counterweights. After the quenching the forging is preferably reheated in the usual'manner to a temperature below the Ac thermal critical or about 1000 to 1100 F., depending on the analysis of the steel, in order to permit the transformation to complete itself to the desired stage and thereby produce the proper combination of physical properties in the forgmg.

My invention is particularly advanta eous for use in the manufacture of multi-t row crankshafts having counterweights formed integral therewith, whether the throws are in the same or different planes. The peculiarform of these crankshafts and the posiy any of the usual methods extremely difficult. With my a paratus all the counterweights may be coo ed simultaneously and uniform physical properties may be easily obtained.

's method is suitable for use with all kinds of steel except what is familiarly known as air hardening steel, and is particularly adapted for steel running about .40 to .50 per cent carbon, which is that'most comsteel articlesinwhich difierential hardening is desirable. The form and arrangement of the apparatus will naturally depend upon the particular article to be treated.

I claim as my invention 1. The method of treating articles of steel which consists in heating the article to a temperature above the Ac thermal critical temperature, slowly cooling certain portions of the article below the hardening range while retaining the remaining portions within this range, and then subjecting the article in this condition to quenching.

2. The method of treating articles of steel which consists in heating the article above the Ac thermal critical temperature, slowly cooling certain portions of the article to a temperature below the Ar thermal critical temperature while retaining the remaining portions at atemperature above the Ar thermal critical temperature, subjecting the article in this condition to quenching and then reheating the article to a temperature below the Ac thermal critical temperature.

3. The method of treating articles of steel which consists in heating the article above the Ac thermal critical temperature, cooling certain portions of the article below the hardening range by means of an a1r blast while retaining the remaining portlons wi in this range, and then subjecting the arti le in this condition to quenching.

4? The method of treating articles of steel which consists in heating the article to a temperature above the Ac thermal critical temperature, cooling certain portions of the article below the hardening range by means of an air blast directed on these portions and regulated to cause the; cooling to take place at a rate sufficiently slow to insure a complete transformation of the metal in these portions to a pearlitic, sorbiti c or pearlitic-sorbitic condition, the remaining portions of the article being retained at a temperature within the hardening ran e during said cooling, subjecting the artlc e in this condition to quenching, and then reheating the article sufiiciently to permit the transformation to complete itself to the desired stage.

5. The method of treating articles of steel which consists in heating the article above the Ac thermal critical temperature, cooling certain parts of the article to a temperature below the Ar thermal critical temperature by means of an air blast applied d1- rectly to these parts and regulate to cause the cooling to take place at a rate sufiiciently the crankshaft bein slow to insure a complete transformation of the mass of metal composing these parts to a pearlitic, sorbitic or pearlitic-sorbitic condition, the remaining parts of the article being retained at a temperature above the Ar thermal critical temperature during the cooling operation, subjecting the article in this condition to quenching, and then reheating the article to a temperature of from 1000 F. to 1100 F., depending on the analysis of the steel, to ermit the transformation to complete itself to the desired stage.

6. The method of treating multi-throw crankshafts having counterweights formed integral therewith which consists in heating the crankshaft to a temperature above the Ac thermal critical temperature, cooling the counterweights to a temperature below the hardening range while retaining the remaining portions of the crankshaft within said range, and then subjecting the crankshaft in this condition to quenching.

7. The method of treating multi-throw crankshafts having counterweights formed integral therewith which consists in heating the crankshaft to a temperature above the Ac thermal critical temperature, cooling the counterweights by means of an air'blast to a temperature below the hardening range while retaining the remaining portions of the crankshaft within said range, subjecting the crankshaft in this condition to quenching, and then reheating the crankshaft to a temperature below the Ac thermal critical temperature.

8. The method of treating multi-throw' crankshafts having counterweights formed integral therewith which consists in heating the crankshafts to a temperature above the Ac thermal critical temperature, cooling the counterweights to a temperature below Ar thermal critical temperature by means of an air blast directed at these parts and regulated to cause the cooling to take place at a rate sufficiently slow to insure a complete transformation of the metal of the counterweight to a pearlitic, sorbitic or pearliticsorbitic condition, the remaining portions of retained at a temperature above the Ar t ermal critical temperature, subjecting the crankshaft in this condition to quenching, reheating the crankshaft to a temperature below the Ac thermal critical temperature, and then permitting the crankshaft to cool. i

9. The method of treating multi-throw crankshafts having counterweights formed integral therewith which consists in heating the crankshaft proper and counterweights above the Ac, thermal critical temperature, simultaneously cooling the counterweights to a temperature below the Ar thermal critical temperature by means of air blasts directed at each of the counterweights, the crankshaft proper bein maintained at a temperature above the r /thermal critical tem erature, quenching the crankshaft while in his condition, and reheatin the crankshaft to a temperature below t 1e Ac thermal critical to ermit the transformation to com lete itselfi-to the desired stage.

10. p aratus for treating articles of steel having projecting parts comprising a support for the heated article, projectors located about said support and arranged to direct an air blast upon saidparts wi hout subjecting the remaining portions of the article thereto, and means for supplying air under ressure to said projectors.

1.1. i pparatus for treating articles of steel having projecting parts comprisinga support for the heated article, a plurality of projectors arranged about said support and adapted to direct air blasts upon opposite sides of said parts to cool said parts without materially coolin the remaining portions of the article, eac of said rojectors comprising a casing having per orations in one wall directed at the particular part of the article to be cooled thereby, and means for supplying air under pressure to said projectors.

12. Apparatus for treating, integrally counterweighted crankshafts comprising a support for a heated crankshaft, projectors arranged about said support adjacent to the counterweight positions to direct an air blast upon the counterweights in such position without materially cooling the crankshaft proper, and means for supplying air under pressure to said projectors.

13. Apparatus for treating integrally- HAROLD F. WOOD. 

